It is well known in the prior art to manufacture steel tooling and tool inserts for use in injection molding fixtures to produce net shape complex metal and plastic parts in high volume. However, conventional manufacture of such tooling and inserts from wrought metal stock is very costly and time consuming, typically taking up to 28 weeks to manufacture, and requiring large amounts of precision machining for each insert. Each tool insert is usable to manufacture one shape of part.
The present invention overcomes these shortcomings by disclosing production of steel tool inserts by a metal injection molding process described hereinafter, which offers significantly faster cycle times and is relatively inexpensive compared to conventional production of steel tools. Costly machining is eliminated or greatly reduced and is replaced by a near net shape injection molding process.
The production of sintered parts from "green" bodies is well known in the prior art. Generally the green body is formed by filling a die with a powder/binder mixture and compacting the mixture under pressure. The green body, which is a self-supporting structure, is then removed from the die and sintered. During the sintering process, the binder is volatilized and burned out. The sintered part is typically not fully dense (approximately 85-90% of theoretical density) and has substantially reduced mechanical properties compared to wrought material.
Injection molding is a preferred process for manufacturing complex, near-net shape parts from metal and ceramic powders. The tools for producing injection molded parts are generally made from metals such as tool and stainless steels due to the high pressures and temperatures normally required for metal and ceramic feedstock materials. As previously mentioned, conventional manufacture of metal tooling from wrought metal frequently involves long turnaround times, a great deal of precision machining and is very costly.
Injection molding fixtures, which are well known in the art, are designed to interchangeably accept different tool inserts and to be attached to injection molding machines, thus providing highly cost effective production of near-net shape, complex metal, ceramic and plastic parts in high volume.